How are they similar? How are they different? How is each useful in determining the age of rock layers?

2018 means 2018 ce or common era

there have been other eras too including bce, which included way more years.

then your answer is a

hoped that

the viking voyages took place during the middle ages, which was about this time. 500 to 1350. the viking voyages took place during the middle ages, which was about this time.